Printing press having a dryer device for varnished sheets

ABSTRACT

A printing press and a method of drying printed or varnished sheets in a printing press include heating printed and/or varnished sheets, before the sheets enter a dryer, to a temperature higher than the ambient temperature, through the use of a heatable impression cylinder in the last printing and/or varnishing unit upstream of the thermal dryer device.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of U.S. application Ser. No. 11/954,150filed Dec. 11, 2007; the application also claims the priority, under 35U.S.C. § 119, of German Patent Application DE 10 2006 058 238.1, filedDec. 11, 2006; the prior applications are herewith incorporated byreference in their entirety.

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

The invention relates to a printing press including a plurality ofprinting or varnishing units and a dryer device for drying printed orvarnished sheets. Multi-color printing presses with additionalvarnishing unit(s) usually include a dryer device in which the layer ofink or varnish that has been applied is dried before the sheets aredeposited on a sheet stack. It is not easy to dry the sheet sufficientlyin the short time it remains in the dryer device, in particular ifaqueous dispersion varnish is used. At the high machine speeds of 16,000or 18,000 sheets per hour that are common today, the sheets frequentlystay in the dryer for less than a second. One attempt to counteract thishas been to manufacture machines with what is known as an “extendeddelivery” and to provide a plurality of dryer modules following eachother in the delivery of the printing press, typically 3 to 4 dryermodules. Moreover, two or more drying towers are frequently used insteadof just one drying tower for additional drying of the sheets between twovarnishing units. Another attempt has been to increase the dryingperformance by increasing the temperature and/or the hot air stream. Forinstance, in machines of the 70/100 format, it is not uncommon today touse a dryer device with a wattage of more than 100 kW in the deliveryand even 125 kW in the drying towers between the varnishing units and toextend the dryer section in the delivery to 4 m.

However, increasing the wattage of the dryer devices does not make sensein economic terms because a large proportion of the energy is not usedto evaporate the solvents from the ink or the water from the layer ofvarnish, but is lost as waste heat. On one hand, this is due to the factthat the degasification or evaporation process does not start at fullstrength when the sheet enters the dryer because a large proportion ofthe energy is required initially to heat up the sheet of paper itself.On the other hand, the measure of extending the delivery and addingdryer units considerably increases the installation space required forsuch a printing press. Apart from the fact that such a measure becomesimpossible in some cases for reasons of space limitations, an additionaldryer unit or an extended delivery means additional costs that increasethe price of the printing press.

It is known from International Patent Application No. WO 01/68223 A1,corresponding to U.S. Pat. No. 6,868,788, to use the waste heat of theprinting press for pre-heating the air of a thermal dryer. However, thatmeasure is insufficient to solve the problems indicated above, i.e. thehigh energy consumption of the dryer itself and the long dryer sections.

Another option is the introduction of what are known as “interdeckdryers” into every printing unit in question to dry the ink or varnishdirectly at that location. Apart from the fact that such a measure ishighly complex, such interdeck dryers have their drawbacks inasmuch asthe sheets are heated up during an ongoing printing operation. That mayhave a negative effect on the quality of the printed image because theconditions in the press during a printing operation are desired to be asuniform as possible. As a consequence, additional steps must be taken,for example to compensate for an uneven heating up of an impressioncylinder equipped with an interdeck dryer, as described in GermanPublished, Non-Prosecuted Patent Application DE 10 2005 022 595 A1.Alternatively, cooled blown air is introduced into the path of sheettravel to cool down the sheet in the subsequent printing unit to thedesired temperature for the printing operation, as described in EuropeanPatent Application EP 1 502 738 A1, corresponding to U.S. Pat. No.7,044,059.

For those reasons, interdeck dryers are usually not thermal dryers, butmainly UV dryers used in connection with printing inks that harden underthe influence of ultraviolet light.

Furthermore, German Published, Non-Prosecuted Patent Application DE 10305 594 A1 discloses an interdeck dryer wherein the impression cylinderof a printing or varnishing unit is heated up.

European Patent EP 1 287 204 B1, corresponding to U.S. Pat. No.7,017,493, describes heated smoothing rollers for treating the printedor varnished sheet surface and for heating up the printed sheet.However, that document also describes additional cooling rollers forcooling down the printing material or printed sheet after the smoothingoperation. The problems of the dryer that have been described above arenot dealt with in that document.

BRIEF SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide a printing pressand a method of drying printed or varnished sheets in a printing press,which overcome the hereinafore-mentioned disadvantages of theheretofore-known devices and methods of this general type, which improvethe drying of the sheets in a sheet-fed printing press and which makethe drying operation more efficient.

With the foregoing and other objects in view there is provided, inaccordance with the invention, a method of drying printed or varnishedsheets in a sheet-fed printing press. The method comprises providing aplurality of printing and/or varnishing units and a dryer device, andheating the sheets to a temperature higher than the ambient temperaturebefore the sheets enter the dryer device.

This ensures that the degasification or evaporation process starts assoon as the sheet enters the dryer device and is subjected to hot airand/or infrared radiation. Due to this measure, the length of the dryersection can be shortened considerably and the energy required by thedryer device can be reduced, an aspect that is of particular importancein terms of dryers that use infrared radiation because they have arelatively low efficiency factor of about 25% anyway.

In accordance with another mode of the invention, it is expedient forthe sheet to be heated up to a temperature above the temperature of theprinting units in the printing press, for example to a temperature inthe range between 25° C. and 50° C. (approximately between 77° F. and122° F.), preferably between 32° C. and 45° C. (approximately between90° F. and 113° F.), because this is the temperature range to which thepaper that passes through a hot-air dryer or a radiation dryer isapproximately heated up in an asymptotic way in the sense of what isknown as a “persistence temperature” until the sheet leaves the dryer.The persistence temperature is the temperature that the sheet assumeswhile the ink is degasified or the wetness is evaporated from the layerof varnish. In the process, a balance is reached between the heat thatis being supplied by the hot air or infrared radiation and the heat thatis being output due to the evaporation of the wetness and solvents.

In accordance with a further mode of the invention, it is expedient forthe sheets to be heated up by a heated impression cylinder, mostadvantageously by the impression cylinder of the last printing orvarnishing unit upstream of the dryer device as viewed in the directionof sheet travel. Direct contact between the impression cylinder and thesheet ensures a highly effective temperature transfer. In addition, thesheet does not have time to lose the acquired temperature again beforeentering the dryer.

In accordance with an added mode of the invention, it is particularlyadvantageous to use the waste heat of the dryer to preheat the sheetwith the aid of the impression cylinder since the temperature of thewaste heat of hot-air dryers generally ranges between about 50° C. and80° C. (approximately between 122° F. and 176° F.) and can be useddirectly, i.e. without the use of additional heat pumps, to heat theimpression cylinder.

In accordance with an additional mode of the invention, in order tostabilize the printing process, it may furthermore be advantageous toheat up or warm up further cylinders in the path of sheet travel inaddition to the impression cylinder in the last printing unit upstreamof the dryer device. An especially advantageous feature is to heat upthe sheets to a temperature of 25° C. (approximately 77° F.) as early ason the feed table, to even out temperature fluctuations of the feederstacks that are being supplied. The temperature of the additionalcylinders and/or of the feed table may also be increased by using thewaste heat of the dryer device.

With the objects of the invention in view, there is also provided asheet-fed printing press, comprising a dryer device for thermally dryinga layer of ink and/or varnish printed onto sheets, and a plurality ofprinting and/or varnishing units including a last printing or varnishingunit disposed upstream of the dryer device in sheet travel direction.The last printing or varnishing unit has a heatable impression cylinderwith an operating temperature selected in such a way that the sheetsleaving the impression cylinder have been heated to a temperature higherthan the ambient temperature as the sheets enter the dryer device.

Other features which are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is illustrated and described herein as embodiedin a printing press and a method of drying printed or varnished sheetsin a printing press, it is nevertheless not intended to be limited tothe details shown, since various modifications and structural changesmay be made therein without departing from the spirit of the inventionand within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however,together with additional objects and advantages thereof will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a diagrammatic, longitudinal-sectional view of a conventionalsheet-fed printing press with a plurality of printing and varnishingunits and a dryer device including a drying tower and an extendeddelivery;

FIG. 2 is a view of the printing press of FIG. 1 modified in accordancewith the invention; and

FIGS. 3 and 4 are diagrams illustrating a degasification behavior ofwetness from a varnished printed sheet as the sheet passes through thedryer.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the figures of the drawings in detail and first,particularly, to FIG. 1 thereof, there is seen a straight-printingsheet-fed offset printing press 1 of in-line construction, i.e. aprinting press for printing on only one side of the sheets. The printingpress 1 includes a feeder 2 with a stack 3 of unprinted paper sheetsdisposed therein and six printing units 8 a to 8 f for the four processcolors and for two optional special or spot colors, a first varnishingunit 9 a, followed by two drying towers 10 a and 10 b, a secondvarnishing unit 9 b, and a delivery 5 for a sheet stack 6. In the regionof chain guides of the delivery 5, four further interdeck dryers 11 a to11 d are inserted between the chain guides in the delivery that has beenextended in a corresponding way.

Reference numerals 4 a to 4 f designate impression cylinders of theprinting units, reference numerals 14 a and 14 b those of the varnishingunits, and reference numerals 17 a and 17 b those of the drying towers.In cooperation with the impression cylinders, transfer drums 5 b to 5 fprovided between the printing units, transfer drums 5 g and 5 j providedupstream of the varnishing units 9 a and 9 b, and transfer drums 5 h and5 i provided upstream of the drying towers, convey the printed sheetsthrough the press.

The drying towers 10 a and 10 b are combined hot-air dryer and infraredradiator units for drying aqueous dispersion varnish applied in thevarnishing unit 9 a before the second varnishing unit 9 b applies asecond layer of varnish onto the dried first layer of varnish. Each ofthe two drying towers 10 a and 10 b has an electrical connection powerof 60 kW.

The interdeck dryers 11 a to 11 d are likewise constructed as combinedinfrared radiation/hot-air dryers. They are available from HeidelbergerDruckmaschinen AG under the trademark “DryStar 3000” and have a maximumelectrical connection power of 66 kW per inserted unit.

A printing press of this type is available, for example, fromHeidelberger Druckmaschinen AG under the trademark “Speedmaster XL105-6-LYYLX3” for the 75×105 cm format. The press has a total length of21 m. The dryer section requires 5.3 m of this total length for thedrying towers 10 a and 10 b and the interdeck dryers 11 b to 11 d in theextended delivery.

FIG. 2 shows this press in an embodiment that has been modified inaccordance with the invention. The drying tower 10 b has beeneliminated, and the extended delivery including the four interdeckdryers 11 a to 11 d has been replaced by a shortened delivery 15. Thelength of the dryer section has been cut in half since it only uses twointerdeck dryers 11 a and 11 b. Otherwise, machine parts that areidentical with those shown in FIG. 1 are identified by identicalreference numerals and will not be explained in detail again.

The exhaust air of the drying tower 10 a and of the interdeck dryers 11a and 11 b is fed to a cooler 22 through exhaust pipes 21 a and 21 b. Inthe cooler 22, the hot exhaust air, which has a temperature of about 70°C. (approximately 158° F.), heats up an infeed line 30 of a hot-watercircuit or system through a heat exchanger 23. The circuit includes aninfeed line pump 25, a motor-driven three-way valve 24 and a hot-wateror heat reservoir 26. Temperature sensors 27 are provided on the heatreservoir 26, temperature sensors 28 are provided at an outlet of thecooler 22 and a temperature sensor 29 is provided in the infeed line 30of the hot-water heating system. These temperature sensors 27, 28, 29control the motor-driven three-way valve 24 in such a way that theunneeded surplus heat emitted by the cooler 22 heats up the heatreservoir 26, which feeds an increasing amount of warm water into theinfeed line 30 in times when the heat supply is insufficient.

The hot-water circuit heats the impression cylinders 14 b and 14 a ofthe two varnishing units 9 b and 9 a and a table 112 of the sheet feeder2.

The impression cylinder 14 b of the varnishing unit 9 b is supplied withhot water at an infeed line temperature of about 60° C. (approximately140° F.) through a supply line 31. The temperature is monitored by atemperature sensor 32 b and controlled in a closed loop through the useof a first mixing valve 33 b. The water that returns from the impressioncylinder 14 b through a return line 34 has a lower temperature of about50° C. (approximately 122° F.) and is fed through a second mixing valve33 a to an inlet 35 of the impression cylinder 14 a of the firstvarnishing unit 9 a. In this case, too, a sensor 32 a is provided formeasuring the feed temperature.

The impression cylinders 14 a and 14 b may be provided with a rotaryfeedthrough for the hot-water connection and a piping system disposed inthe cylinder walls as is described, for example, in German Published,Non-Prosecuted Patent Application DE 10 2005 022 595 A1.

The water being fed back from the impression cylinder 14 a through areturn line 36 is fed through a third mixing valve 38 to an infeed line39 for the heated sheet feed table 112, at a temperature of about 30° C.(approximately 86° F.). In this case, too, a sensor 37 measures thetemperature in the supply line 39. A return connection of the feed table112 leads to a return line 40 leading to the heat exchanger 23 in thecooler 22.

The mixing valves 33 a, 33 b and 38 are actuated by a control unit 42 inaccordance with signals from the temperature sensors 32 a, 32 b and 37to maintain temperatures T1 in the infeed line 31, T2 in the inlet orinfeed line 35 and T3 in the infeed line 39 at the aforementioned levelsof 60° C. (approximately 140° F.), 50° C. (approximately 122° F.), and30° C. (approximately 86° F.), respectively. An additional heater 41,which is likewise connected to the control unit 42, is switched on bythe control unit 42 in cases in which the temperature of the hot watersupplied by the cooler 22 or by the hot-water reservoir 26 is notsufficient, for example when a print job is started and the hot-waterreservoir is cold.

The device operates as follows: When the sheets transported through theprinting press by the transfer drums 5 b to 5 g and by the impressioncylinders 4 a to 4 f in the printing units 8 a to 8 f reach thevarnishing unit 9 a, the sheets have a temperature of about 25° C. to30° C. (approximately 77° F. to 86° F.). What is taken into accountherein is the fact that the printing units approximately assume thistemperature due to the waste heat generated in the printing units. Thus,this temperature is the ambient temperature for the printed sheetsconveyed through the press. In order to maintain this temperature rightfrom the start in view of a stable printing process, the feed table 112is heated by water of a temperature of approximately 30° C.(approximately 86° F.). Consequently, the sheets that are taken off thepaper stack in the feeder 2 have the desired temperature ofapproximately 25° C. (approximately 77° F.) when they reach the firstprinting unit 8 a and can be printed at this temperature even if thestacks that are supplied to the feeder 2 are cold.

The sheets that have been printed on and provided with a first layer ofvarnish are heated up to a temperature of about 37° C. (approximately99° F.) by contacting the impression cylinder 14 a in the firstvarnishing unit 9 a. This temperature of 37° C. (99° F.) corresponds tothe persistence temperature which the paper sheets would have beenheated up to after passing through the two drying towers 10 a and 10 bof the press shown in FIG. 1 if they had entered the first drying tower10 a at the ambient temperature of about 25° C. (approximately 77° F.).For a paper sheet of a grammage of 135 g/m² in the 75×105 format,heating up the sheet from the rear side through the use of theimpression cylinder 14 a by about 12° C. corresponds to an energy inputof about 1.66 kJ. At a press speed of 18,000 sheets per hour, i.e. 5sheets per second, this is equivalent to an electric wattage of 8.3 kWif we assume that the drying towers have an efficiency factor of η=1.However, this is not the case with IR radiators, for example. They havean efficiency factor of about 25%.

Thus, the second drying tower 1 Ob can be dispensed with.

Once the sheets have passed the drying tower 10 a, they are varnishedonce more in the second varnishing unit 9 b, where they are contacted bythe impression cylinder 14 b having a temperature of 60° C.(approximately 140° F.). They reach the impression cylinder 14 b at atemperature of about 37° C. (approximately 99° F.) and are heated up byabout 7° C. (12° F.) to a temperature of 44° C. (approximately 111° F.).This ensures that the wetness of the second layer of varnish begins toevaporate virtually immediately as the sheets enter a first module orinterdeck dryer 11 a of the dryer unit formed by two modules orinterdeck dryers 11 a and 11 b in the delivery 15. The interdeck dryers11 c and 11 d additionally provided in the press shown in FIG. 1 can bedispensed with because the measures described herein ensure that adrying section shortened almost by half is sufficient. However, thesheets may also be delivered at a temperature that is lower than the 44°C. (approximately 111° F.) entry temperature (stack temperature) if thedelivery dryers dry mainly convectively (i.e. exclusively by hot air)and the temperature of the hot air is selected in such a way that apersistence temperature of less than the aforementioned temperature of44° C. (approximately 111° F.) is achieved.

The effect attained by the invention will best be understood withreference to the diagrams shown in FIGS. 3 and 4. FIG. 3 shows thetemperature increase Ts of a varnished sheet in a hot-air dryer having atemperature THA Of 100° C. (approximately 212° F.), assuming that thesheet enters the dryer at a temperature of 20° C. (approximately 68°F.). After 0.4 sec, which is the amount of time a sheet needs to passthrough a typical 1.6 m drying section at a printing speed of 15,000sheets per hour, the temperature of the sheet has increased to 32° C.(approximately 90° F.), i.e. by about 12° C. (about 22° F.). The diagramalso shows the evaporation of the wetness from the layer of varnish as afunction of time. The evaporation rate strongly depends on thetemperature of the sheet, i.e. of the paper substrate. It converges atapproximately 4 g/m²sec at an assumed sheet temperature of 34° C.(approximately 93° F.). However, this temperature is never reached fullybecause at this point in time the sheet has long since left the dryer.The amount of evaporated water corresponds to the shaded area below theevaporation rate identified by reference symbol ER.

In contrast, FIG. 4 illustrates a case wherein the sheet has alreadyreached a temperature of 34° C. (93° F.) when it enters the dryer. Inthis case, an evaporation rate of 4 g/m²sec is achieved right from thestart and the amount of water expelled or evaporated in the dryer isalmost twice as high.

The present invention has been described with reference to an exemplaryembodiment referring to a straight-printing press with two varnishingunits. However, it may likewise be used in presses with just onevarnishing unit or in perfecting presses, for example in pressconfigurations wherein a varnishing unit and a dryer unit are providedupstream of the reversing device or upstream of the first printing unitof the straight-printing portion of the press to keep the drying sectionat these locations short. Moreover, the invention can also be used inconnection with sheet-fed printing presses without a varnishing unit toeffectively dry conventional inks for wet-offset printing or thelower-viscosity anilox inks that are applied by short inking unitsincluding a screen roller and a chambered doctor blade. In this case,the sheets are pre-heated through the use of the impression cylinder ofthe last printing unit before they enter the dryer. This ensures thatthe evaporation of the solvent proportion of the anilox inks startsimmediately after the sheets enter the dryer unit.

1. A sheet-fed printing press, comprising: a dryer device for thermallydrying a layer of ink and/or varnish printed onto sheets; a plurality ofprinting and/or varnishing units including a last printing or varnishingunit disposed upstream of said dryer device in sheet travel direction;said last printing or varnishing unit having a heatable impressioncylinder with an operating temperature selected to cause the sheetsleaving the impression cylinder to have been heated to a temperaturehigher than ambient temperature as the sheets enter said dryer device.2. The printing press according to claim 1, which further comprisesfurther heatable cylinders in said printing and/or varnishing unitsother than said last printing or varnishing unit.
 3. The printing pressaccording to claim 1, which further comprises a heatable sheet feedtable.
 4. The printing press according to claim 1, which furthercomprises other sheet-guiding cylinders, said operating temperature ofsaid heatable impression cylinder being higher than a temperature ofsaid other sheet-guiding cylinders.
 5. The printing press according toclaim 4, wherein said operating temperature of said impression cylinderranges between 40° C. and 80° C.
 6. The printing press according toclaim 4, wherein said operating temperature of said impression cylinderranges between 45° C. and 65° C.
 7. The printing press according toclaim 1, wherein said dryer device is at least one device selected fromthe group consisting of a hot-air dryer and an infrared radiation dryer.8. The printing press according to claim 1, which further comprises aheat exchanger receiving exhaust air from said dryer device and beingconnected to said heatable impression cylinder.
 9. The printing pressaccording to claim 8, which further comprises a fluid heated by saidheat exchanger and flowing through said heatable impression cylinder.